chrome.runtime.sendMessage({greeting: "hello"}, function(response) {
  console.log(response.farewell);
});

chrome.runtime.onMessage.addListener(
  function(request, sender, sendResponse) {
    console.log(sender.tab ?
                "from a content script:" + sender.tab.url :
                "from the extension");
    if (request.greeting == "hello"){
      sendResponse({farewell: "I'm contentscript,goodbye!"});
	  }
  });
